Electron discharge device



June 4, 1963 w. 'r. MILLIIS 3,092,749

ELECTRON DISCHARGE DEVICE Filed April 15, 1960 HIGH TENSILE STRENGTHMATERIAL FIG. 2

INVENTOR. WALTER T. MILLIS United States The invention relates toelectron discharge devices and more particularly, to electron dischargedevices of the type having a heated electron emissive surface.

In electron discharge devices or tubes of the type having heatedelectron emissive surfaces or cathodes, difficulty may be encounteredduring tube operation from undesired primary emission of electronsemanating from surfaces other than the cathodes, such as, for example, agrid. During the use of a tube, electron emissive material of a cathodemay evaporate and become deposited on other internal tube structures. Atthe high operating temperatures that may be encountered during electrondischarge device or tube operation, the cathode material that may bedeposited on the various internal tube structures may act as a primaryemitter of electrons.

To reduce the undesired electron emission from the deposited material onthese structures, the operating temperatures of the structure surfacesmay be reduced. Several methods have been proposed for reducing internaltube structure temperatures; however, the methods now in use generallyhave several disadvantages. For example, it has been the practice thatalloys such as chrome copper be utilized in various grids as supportssince such material is an excellent thermal conductor. Although thestructure temperature may be reduced by the utilization of such amaterial, the material itself fails metallurgically, that is, it is toosoft to be capable of manufacture in small Wire sizes as required forsome tube element structures such as grid wires. The use of tungsten ormolybdenum, unplated, or plated with gold or silver, has been used asgrid lateral wire, but is undesirable for manufacture because of costand inherent difiiculty of fabrication. When unplated, these materialsform oxides at relatively low temperatures, which oxides are volatileand tend upon evaporation to deposit on the cathode causing destructivecathode poisoning. Further, gold and silver plating have high vaporpressures at normal tube operating and processing temperatures and thustend to cause inter-element leakage, together with an increase inprimary emission during the life of the discharge device or tube as theplatings evaporate. Several other suggestions have been made to reduceinternal tube structure temperature, and all suggestions have hadserious shortcomings either in the performance of the tube constructedwith these materials orin the capability of the materials to be producedin small sizes suitable for the various internal structures.

It is therefore an object of the invention to provide an electrondischarge device having improved operating characteristics.

It is another object of the invention to provide a material suitable foruse in the formation of structural elements of an electron dischargedevice.

It is another object of the invention to provide a material having ahigh thermal conductivity and a high tensile strength at the operatingand processing temperatures of electron discharge devices.

It is still another object of the invention to provide an improvedmaterial useful in electron discharge device internal structures andthat is capable of being produced in extremely small sizes.

It is a further object of the invention to provide a durable, dependableand relatively inexpensive grid electrode material for use in electrondischarge devices.

Briefly stated, in accordance with one aspect of the invention, thevarious internal structures of an electron discharge device, such as agrid electrode, are constructed of a laminar material having a core ofhigh thermal conductivity material clad with a coating or plating ofhigh tensile strength metal. The proper relationship between tensilestrength and thermal conductivity may be provided by controlling therelative percentage of core-tocladding cross-sectional areas.

The invention both as to its organization and operation together withfurther objects and advantages thereof may best be understood byreference to the following description taken in connection with theaccompanying drawings in which:

FIG. 1 shows a partial fragmentary view of an electron discharge deviceincorporating the teachings of the invention.

FIG. 2 is a cross-sectional view of the grid wire shown in FIG. 1.

Referring to FIG. 1, an electron discharge device is shown in a partialfragmentary view. An envelope 1 is provided with a pair of insulatingsupport members 2. Support members 2 secure a tubular plate elec rode 3in a fixed relation to a cathode electrode 4 and a grid electrodestructure 5. The grid structure 5 may be formed by securing a helicallywound grid wire 6 on a pair of spaced vertical grid support rods 7. Thecathode 4 may be coated with a suitable electron emissive materialwhich, when heated, will readily emit electrons. To provide a heatsource, the cathode 4 may include a filament 8 which is adapted to beconnected to a suitable source of potential (not shown).

It is well known that during the operation of an electron dischargedevice such as shown in FIG. 1, the electron emissive material coated onthe cathode will to some extent evaporate and become deposited onvarious other internal structures of the tube. For example, the emissivematerial may become deposited on the grid wires 6. =It will be apparentto those skilled in the art that any internal structure such as the gridwires 6 having emissive material deposited thereon may become a sourceof primary emission if the structure attains the required temperature.To alleviate such difiiculties, it is desirable that the temperature ofthe affected surface, in this case the grid, be kept as low as possible.

Referring to FIG. 2, an enlarged cross-section of one of the grid wiresof FIG. 1 is shown constructed in accordance with the teachings of theinvention. A core 10 of high thermal conductivity material, such ascopper, is utilized to provide the required high thermal conductivityfor rapidly carrying away the heat and thus reduc ing the temperature ofthe grid. The core 10 is clad or plated with a suitable material 11having high tensile strength at elevated temperatures to provide thestrength necessary to maintain the shape of the grid electrode structureat operating temperatures and also to enable the grid electrode to bemanufactured by high-speed winding as found in modern techniques withoutbreaking. The cladding material 11 is preferably of a material having arelatively high tensile strength and an ability to be cold worked.Exmples of such suitable cladding materials are: Inconel, Inconel 702,Inconel 713, Udimet 500, and Nichrome V. The trade-named materialsstated above as examples, according to standard handbooks of metallurgy,have the following percentage compositions by weight:

3 Inconel: Percent Chromium 13.518. Iron 6.5-9. Nickel Balance. Inconel702:

Chromium 14-47. Aluminum 2.75-3.75. Titanium 0.25-1.0. Iron 1.0. NickelBalance. Inconel 713:

Chromium 11-14.

Molybdenum 3.5-5.5. Titanium 0.25-1.25.

Aluminum 5.5-6.5. Iron 5.0. Nickel Balance. Udimet 500:

Chromium 17.5.

Nickel 53.0. Molybdenum 4.0. Cobalt 16.0. Titanium 3.0. Aluminum 2.5.Nichrome V:

Chromium 18-22. Nickel Balance.

These materials are further characterized in that they possess arelatively high resistance to oxidation at the normal operating andprocessing temperatures of the electron discharge devices in which thegrid is incorporated.

The relative percentage of cross-sectional area of the high thermalconductivity core and the high tensile 7 temperature of operation of thegrids with clad Wire sizes as small as 2 /2 mils. Generally, it isnecessary to increase the proportion of high tensile strength materialas the size of the clad Wire decreases to enable the clad wire towithstand the relatively high 'tensile stress during.

winding operation and to maintain its form at the high operatingtemperature. A relative cross-sectional area of 20% copper and 80%Inconel has been found to have excellent thermal conductivity andadequate tensile strength in overall Wire sizes of from about 1 mil tothe merely indicative of the many advantages to be gained through theuse of the invention. It will be understood by those familiar with theart that structures having high thermal conductivity cores and having ahigh tensile strength cladding thereon may be utilized in other parts oftube structures, such as the grid electrode supports 7 FIG. 1), and willbe equally advantageous in any circumstance where deposition of emissivematerial causes undesired primary emission from surfaces within anelectron discharge device. 7

While I have shown and described specific embodiments of my invention, 1do not desire my invention to be limited to the particular forms shownand described, and I intend by the appended claims to cover allmodifications Within the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is: V

1. A grid electrode for an electron discharge device having a thermioniccathode and an anode supported in an evacuated envelope and in mutuallyspaced relation thereto, means supporting the grid electrode betweensaid cathode and said anode in close proximity to said cathode so thatthe grid is subject to being rendered electron-emissive during operationof the device, said grid electrode comprising a plurality of lateralwires mounted on said supporting means, said wires comprising a core ofcopper material and a cladding of high-tensile strength materialcompletely encasing said core, the relative crosssectional areas of saidcore and said cladding being in the range of about 4 to about 7 toelTect cooling of said grid below electronemissive temperatures andsimultaneously to provide sufiicient structural strength of said grid towithstand tensile stresses exerted thereon during fabrication andoperation of the device.

2. The grid electrode as defined in claim 1, further characterized inthat said core material, at the temperature of fabrication and operationof the device, is normally subject to the formation of oxides of copper,said cladding operating to minimize the formation of such oxides,thereby to avoid adversely afiecting the vacuum condition within saidenvelope. 7

3. The grid electrode as defined in claim 1, wherein said core material,at the temperatures of fabrication-and operation of said device,-isnormally subject to evaporation and sublimation resulting in undesiredelectrically conductive deposits on insulative surfaces of said device,said cladding operating to prevent such evaporation and the consequentformation of such deposits.

References Cited in the file of this vpatent UNITED STATES PATENTS2,282,097 Taylor May 5, 1942 2,417,459 Eitel Mar. 18, 1947 2,568,705Beck Sept. 25, 1951 2,691,116 Allwine Oct. 5, 1954 2,875,363 Nunan Feb.24, 1959 2,904,717 Kerstetter Sept. 15, 1959

1. A GRID ELECTRODE FOR AN ELECTRON DISCHARGE DEVICEHAVING A THERMIONICCATHODE AND AN ANODE SUPPORTED IN AN EVACULATED ENVELOPE AND IN MUTUALLYSPACED RELATION THERETO, MEANS SUPPORTING THE GRID ELECTRODE BETWEENSAID CATHODE AND SAID ANODE IN CLOSE PROXIMITY TO SAID CATHODE SO THATTHE GRID IS SUBJECT TO BEING RENDERED ELECTRON-EMISSIVE DURING OPERATIONOF THE DEVICE, SAID GRID ELECTRODE COMPRISING A PLURALITY OF LATERALWIRES MOUNTED ON SAID SUPPORTING MEANS, SAID WIRES COMPRISING A CORE OFCOPPER MATERIAL AND A CLADDING OF HIGH-TENSILE STRENGTH MATERIALCOMPLETELY ENCASING SAID CORE, THE RELATIVE CROSSSECTIONAL AREARS OFSAID CORE AND SAID CLADDING BEING IN THE RANGE OG ABOUT 1/4 TO ABOUT 3/2TO EFFECT COOLING OF SAID GRID BELOW ELECTRON-EMISSIVE TEMPERATURES ANDSIMULTANEOUSLY TO PROVIDE SUFFICIENT STRUCTURAL STRENGTH OF SAID GRID TOWITHSTAND TENSILE STRESSES EXERTED THEREON DURING FABRICATION ANDOPERATION OF THE DEVICE.